The present invention is directed to a valve body of elastic material for use in the multiple function valve of a vacuum-operated brake power booster of the type in which the pedal-controlled operating rod slides a valve piston which controls the pressure in the booster chamber and cooperates with the valve body. The valve body comprises two roughly circular cylindrical parts with different diameters which are arranged one behind the other in axial direction and are formed in one piece with a bellows portion that interconnects both parts.
A vacuum-operated brake power booster is known from the German printed and published patent application No. 3047863. This booster is formed with a booster piston and a rod coupled with a brake pedal for operation of a double valve by which an operating chamber of the brake power booster is connectable selectably to under-pressure or to higher differential pressure. A first valve is formed by a valve seat at the booster piston and a sealing ring preloaded in the direction of the valve seat, and a second valve is formed by the same sealing ring and a valve portion which is connected with the rod.
The double valve (also called a multiple function valve or poppet valve) of the known brake power booster has the disadvantage during assembly of frequently not being capable of insertion in the valve housing exactly aligned with the operating rod, i.e. coaxially relative to that rod. Since the valve housing has a relatively low degree of stiffness, the center portion of the multiple function valve which has the shape of a corrugated tube or a bellows (roll fold) bends sideways and consequently fails to be seated on the pertaining valve seat in an unobjectionably tight manner. Even on correct mounting, the portion of the known multiple function valve forming the roll fold often spontaneously tucks in without control leading to the potential effect of premature wear.